As textile substrates age, their color tends to fade or yellow due to exposure to light, air, soil, and natural degradation of the fibers that comprise the substrates. Thus, the purpose of hueing agents is generally to visually brighten these textile substrates and counteract the fading and yellowing of the substrates. Typically, hueing agents may be found in laundry detergents, fabric softeners, or rinse aids and are therefore applied to textile substrates during the laundering process. However, it is important that hueing agents function to visually brighten treated textile substrates without causing undesirable staining of the textile substrates. Cellulosic substrates, in particular, tend to exhibit a yellow hue after exposure to light, air, and/or soiling. This yellowness is often difficult to reverse by normal laundering procedures. As a result, there exists a need for improved hueing agents which are capable of eliminating the yellowness exhibited by ageing cellulosic substrates. By utilizing such improved hueing agents, the life of the textile substrates, such as clothing articles, table linens, etc., may be extended. Unfortunately, current thiophene azo dyes, are not as physically stable as desired. Thus, they require special solvents/handling which can limit liquid dye product and laundry care composition formulation flexibility. In addition, current thiophene azo carboxylate dyes disclosed for use in laundry compositions, either do not provide the desired hueing benefit at the levels that can be used in products, are too costly and/or they build up to an undesirable level, thus overhueing the treated situs over multiple treatment cycles.
The thiophene azo carboxylate dyes disclosed herein and the laundry care compositions comprising same offer advantages over previous efforts in this area, as, unlike previous thiophene azo hueing agents, the present thiophene azo carboxylate dyes comprise a formally charged carboxylate moiety (above its pKa) that allows such dyes to provide enhanced deposition, removal and hue angle, without the negatives of pretreat spot staining on polyurea fibers such as Lycra® and/or excessive cost. While not being bound by theory, Applicants believe that such negatives are avoided as the instant thiophene azo carboxylate dyes interacts with metal ions, for example, in the wash water in a more favorable manner. The aforementioned benefits are offered over a range of fabric types. In short, Applicants recognized the source of the current hueing deficiencies and herein provide the solution to such problem. The hueing compounds disclosed herein also absorb light at a wavelength appropriate to visually neutralize the yellowness of substrates, including textile substrates. These compounds function ideally as hueing agents for substrates, including textile substrates, and may be incorporated into laundry care compositions for use by consumers.